LLM host contract test action

Runs focused safety, runner-staging, playbook, documentation, and fixture checks for the shared LLM host-readiness layer:

bash actions/test.llm-host-contract.sh

The fixture verifies deterministic one-thread-per-physical-core selection, the resulting CPU list and mask, NUMA memory and distance parsing, available memory, and positive Memory Mode classification.

For a source-only review that defers Python fixture execution:

bash actions/test.llm-host-contract.sh --shell-only

The action also rejects model/runtime installation and kernel, swap, sysctl, governor, bootloader, or recursive-ownership mutations from Phase 1.